A metallocene catalyst is configured of a main catalyst of which a main component is a transition metal compound, mainly a Group IV metal, and an organometallic compound co-catalyst of which main component is aluminum or boron. The metallocene catalyst, which is a homogeneous single activation point catalyst, may prepare a polyolefin having a narrow molecular weight distribution and uniform chemical compositional distribution, and stereoregularity, comonomer response, and hydrogen response may be freely adjusted depending on a ligand structure of the metallocene catalyst.
Particularly, in the case of polyethylene, enhanced toughness, strength, environmental stress cracking resistance (ESCR), or the like, may be important. Therefore, a method for preparing a polyolefin having a bimodal or broad molecular weight distribution to enhance mechanical properties that a high molecular weight resin has and processability in a low molecular weight has been proposed.
The polyolefin having a bimodal and broad molecular weight distribution is a polymer having two kinds of average molecular weights, that is, a high molecular weight and a low molecular weight. As a method for synthesizing a polymer having this molecular weight distribution, a method of mixing two different catalysts in a single reactor, or a method of introducing at least two catalysts in a single carrier to perform polymerization have been disclosed.
In the methods for adjusting molecular weight distribution of the polymer according to the related art, generally, at the time of preparing a catalyst, a multi-metal complex is formed using at least two metals, and the molecular weight distribution is improved by adjusting the activation point of each of the metal catalyst components.
However, polymerization only by hybrid of two catalysts has been suggested, and selections of organometallic compounds and homogeneous catalyst systems for controlling the molecular weight distribution and polymer properties have been only mentioned, but there was a limitation in preparing supported catalysts applicable to gas-phase and slurry processes, or the like.